Process for the production of copies of a standardized density

ABSTRACT

Positive photographic images of substantially the same high density and substantially the same low density are produced from negatives having wide range of densities but substantially the same shadow density by printing the negatives on printing material that prints with different contrast when exposed to different colors, but produces substantially the same high density for the same exposure times, and adjusting the exposure proportion to both colors to bring the low density to substantially the same low level.

United States Patent Hellmig et al.

1 Oct. 1, 1974 PROCESS FOR THE PRODUCTION OF COPIES OF A STANDARDIZED DENSITY Inventors: Ehrhard Hellmig, Leverkusen,

Germany; Jacques Leon Vanheerentals', Mortsel, Belgium AGFA-Gevaert Aktiengesellschaft, Leverkusen, Germany Filed: Jan. 28, 1972 Appl. No.: 221,675

Related US. Application Data Continuation of Ser. No. 789,507, Jan. 7, 1969, abandoned.

Assignee:

Foreign Application Priority Data Jan. 20, 1968 Germany 1622255 US. Cl. 96/27 E, 96/44 Int. Cl G03c 5/04, G03c 5/06 Field of Search 96/44, 68, 67, 27 E, 69;

References Cited UNITED STATES PATENTS Hellmig 96/68 3,450,536 6/1969 Wyckoff 96/68 3,628,960 12/1971 Philippaerts et al. 96/27 E 3,753,707 8/1973 Burger et al. 96/27 E FOREIGN PATENTS OR APPLICATIONS 494,088 10/ 1938 Great Britain Primary ExaminerDavid Klein Assistant Examiner-Richard L. Schilling Attorney, Agent, or FirmConnolly and I-Iutz [5 7] ABSTRACT Positive photographic images of substantially the same high density and substantially the same low density are produced from negatives having wide range of densities but substantially the same shadow density by printing the negatives on printing material that prints with different contrast when exposed to different colors, but produces substantially the same high density for the same exposure times, and adjusting the exposure proportion to both colors to bring the low density to substantially the same low level.

4 Claims, 3 Drawing Figures HVVEIJ'TQR.

JAQQUES LEON VANHEERENTAL HHARD HELLMIG 3 PROCESS FOR THE PRODUCTION OF COPIES OF A STANDARDIZED DENSITY This application is in part a continuation of application Ser. No. 789,507 filed Jan. 7, 1969.

The present invention relates to a process for the production of photographic copies of substantially uniform minimum and maximum densities.

Photographic prints which are to be used for producing copies by ink duplicating, such as through the use of a photoresist layer or on so-called pigment paper or on carbon tissue, irrespective of whether the inked duplications are continuous tone images or screen images, must meet certain conditions as regards the minimum or maximum densities, i.e., the densities for thelight and shadow portions, in order to produce the best results. Thus, for example in the field of photogravure printing of variable depth, the original continuous-tone positive photographic prints used for producing copies on pigment paper should have a minimum density of 0.3 0.05 for black-white copies and a density range i.e., the difference in the densities for the light and shadow portions, of 1.35 i 0.05 (DIN 16,602). Similar requirements are applicable to the making of color separation prints and can also be applied to the making of color separation negatives.

ln order to obtain such standard density values within these limited tolerances, continuous tone negatives used to produce continuous tone positive prints should themselves be standardized. According to common practice the best value for the density of the negative is 0.3 for the shadow portions and for the highlights 1.7. If standardized continuous tone positives are to be obtained from negatives outside of these tolerances, the deviations must be compensated as by individual treatment when developing the positives. The production of negatives which are more or less equal in density, or are standardized, generally requires even more careful individual treatment both in the development and in exposure since the originals from which the negatives are produced vary greatly in the density ranges, especially the shadow portions.

Thus, for example, black-white continuous tone reflection originals will normally have densities which range between about 0.7 and 2.0. Transparent originals, e.g. color diapositives (transparencies) from which negative color separation records are to be produced, have even widerdensity ranges (about 0.7 to 3.0). By the terms light and shadow densities are meant the maximum and minimum densities in the negatives, and the minimum and maximumdensities in the positives. Adjusting for these differences hinders efforts to make photographic processes efficient and economical. In particular, automatic development for the production of continuous tone negatives of equal density has been impractical because this only works efficiently if adjusted to run at constand speed, i.e., if the development time is the same for all the negatives regardless of whether the negative has been produced from a high contrast, normal or low contrast original. Reference in this connection is made to U.S. Pat. No. 3,53l,l99 granted Sept. 29, 1970.

' Therefore in this case continuous tone negatives have their highlight densities varying from about 1.0 to 2.5

depending on the density range of the original, i.e., by

more than 1.5 logarithmic units, whilst the densities in the shadow portions remain comparatively constantand, depending on the practical working conditions, show values of only up to about 0.6.

It will readily be seen that if standardized continuous tone positive copies are to be produced from these negatives which have variable densities in the light portions, it will be necessary to employ different exposure times for the production of the copies. Thus, for example, using the 2.5 and 1.0 figures for the highlight densities, the denser negative must be exposed 1.5 times longer, in logarithmic units, than the other, that is to say by the numerical factor 32. Acrually, the exposure times differ by even more than thisfactor of 32 since the increase in length due to the Schwarzschild effect (reciprocity failure) also must be taken into account. For a Schwarzschild exponent of 0.90 or 0.80, the factor of 32 becomes 46 or respectively.

This has the following disadvantages. Since for practical reasons there is a lower limit to the exposure time, very high exposure times for negatives with high densities in the light portion may be necessary. If, for example, the minimum exposure time possible for a particular copying apparatus is 2 seconds, the above mentioned high contrast negative would require an exposure time of at least 64 seconds, which is far too long for practical purposes. High speed shutters that can be adjusted from tenths of a second to a few seconds can be used, but are expensive and the short exposure times involved call for a much more sensitive photographic material or a correspondingly more powerful source of copying light. The maximum sensitivity of a silver halide emulsion layer, however, is limited by the graininess of the silver halide and the dark room inconvenience of handling the unexposed photographic film. If a powerful source of copying light is used this gives rise to additional technical and constructional problems, e.g., the removal of the heat generated by powerful lights.

The most serious disadvantage, however, concerns the photographic copying material since the Schwarzschild effect is not constant over the foregoing extended periods of time but varies in an uncontrollable manner so that the production of standardized copies which will have predetermined density values (e.g. 0.30 and 1.70) in the light and shadow portion cannot be ensured.

It is among the objects of the present invention to provide a simple process for the production of copies of standardized densities from originals which may have any ranges of densities. Additional objects of the present invention include desirable working arrangements for carrying out the foregoing process.

The foregoing as well as other objects of the present invention will now be discussed in the following description of several of its exemplifications, reference being made to the accompanying drawings, wherein:

FIG. 1 shows a set of characteristic curves of a photographic material containing two silver halide emulsions being differently sensitized upon exposure to light of different colors according to the process of the present invention, and

FIG. 2 is a similar graphical representation in connection with a modification of the present invention,

and

FIG. 3 shows the spectral density curves of the filters that can be used in connection with the present invention.

We now have found .a process for the production of positive photographic continuous-tone images having substantially equal low density in the highlights and substantially equal high density in the shadow portions from black-white negative continuous-tone originals of different density range but substantially equal density of the shadow portions which process comprises providing a printing material having two silver halide emulsions of different spectral sensitivities and contrasts, adjusting the sensitivity of the emulsions or the intensity of the copying light to obtain characteristic curves which intersect at the high density value within the range of from 1.5 to 2.0 when given same exposures to lights to which the emulsions are preferably sensitive, printing on said printing material a positive copy of said negative original using substantially the same total exposure time sum of both exposure-times for each negative selecting the proportion of the printing lights to which the printing material is sensitive by only measuring the maximum density of that negative original, so as to provide a contrast range of the positive copy that brings the highlight density to substantially the same low level. v

The process of the present invention results in positive copies which have approximately equal maximum and minimum densities from negative originals which have substantially equal density of the shadow portions (low density areas) but which differ greatly in their density range-in other words in their maximum density by using a printing material having at least two silver halide emulsions of different spectral sensitivities, the 'y-value of the silver halide emulsions varying with the color of the copying light so that a sufficiently flat -y-value is obtained with a light color L, and a sufficiently steep y-value is obtained with another light color L the sensitivities of the silver halide emulsions and/or the intensity of the copying lights L, and/or L used for the exposure being so adjusted to each other that when using the same exposure time for light of the color L, and light of the color L and/or for exposures partly with L, and partly with L the characteristic curves obtained intersect at the level of the desired density value D for the shadow portions in the positive copy. That density value generally is within the range of 1.5-2.0. Sufficiently flat gamma values are within the range of 0.5-0.9, sufficiently steep between 1.3 and and 1.8. Then the process of the invention comprises the following steps: 1.

adjusting the sensitivity of the said silver halide emulsions of the printing material and/or the relative intensity of the copying lights L, and L used for the exposure step so that for a given exposure time to light of color L, or to light of color L and/or partial exposure to L, and L the resulting characteristic curves intersect at a particular high density value within the range of from 1.5 to 2.0 which corresponds to the desired density value D which is to be obtained in the shadow portions of the positive copy, 2.

determination of the density range of the negative original by only measuring the maximum density the minimum density is substantially equal of the negative original by means of a densitometer and selecting the proportions of the printing lights L, and L to which the printing material is sensitive and 3.

exposing the printing material through the negative original with the printing light. The proportions of which have been determined by step 2 wherein substantially the same total exposure time is applied for each negative and further processing the thus exposed printing material by development and fixing according to common practice.

black-white negative continuous tone originals of different density ranges, and the crux of this process is the adjustment of the silver halide emulsions of the printing material and/or the intensity of the printing light as explained above in step 1 of the process.

As to the steps 2 and 3 of the process it is pointed out that they are well known in the art (and not essential to the disclosure of the invention). Reference is made to the articles of Rowland S. Potter Graduation control, PSA Journal, Vol. 18, May 1952, H. Wester Varigam and Multigrade, Camera 28 (1949) p. 149-15l and B. Schwalberg Varigam, Multigrade Popular Photography, Vol. 42 (1958), p. 88-93, further to the broshure of M. R. Marx Printing with Varigram, camera craft publishing comp., San Francisco, first edition.

The desired adjustment of the two characteristic curves produced with light of the color L, or L is obtained with a given photographic material of the above described composition by altering the characteristic curve of that emulsion which is too sensitive into the desired less sensitive position on the log i.t axis by reducing the radiation of the particular color until the point of intersection of the two curves lies at the re quired density value.

When this adjustment has been made, the characteristic curves which are obtained when exposure is carried out for the same total length of time but partly with light of color L, and partly with light of color L either simultaneously or successively, should pass through the same desired density value.

FIG. 1 illustrates the foregoing combination by displaying a set of characteristic curves graphically shown with respect to an ordinate axis representing image density and an abscissa axis representing exposure (lgit; where i =intensity of the copying light, t exposure time). All the curves pass through point P which corresponds to the desired density value for the shadow or high density portions of the copies, in this case 1.6. In the figure, the characteristic curves 1 to 6 represent exposure to the two light colors (L, and L according to the following proportions, given as percentage values:

Light colors Curve L, L,

nate of point P. This is so regardless of which of the characteristic curves is used for any negative.

Such behaviour of a light-sensitive photographic material is unusual since normally no significant change in the gamma-value can be observed when the light color is altered during the production of the copy. A change in gamma can normally only be obtained by changing the development conditions (development time), a method which cannot be used when automatic processing is desired. Furthermore, a set of characteristic curves is obtained, which unlike those obtained here remain practically unchanged in the light portion (on the threshold of the curve) while the shadow portions of the positive show considerable changes. This leads to the disadvantages described earlier when photographic materials are used, the gamma of which varies with the color of the light. It was therefore extremely unexpected that the characteristic curves could be influenced in accordance with the invention by a quite different and new method of adjusting the photographic material to the exposure conditions.

Since the point P lies in the same position for all the curves, all negatives which have the same density in the shadow portions can always be copied with the same exposure time regardless of their density range, the exposure time in this case being the total exposure time (sum of partial exposures required for L and L A photographic material which has been adjusted in this way thus has a constant shadow density which corresponds to the point at which the perpendicular drawn from P in the figure intersects the log i.t axis. The serious disadvantage of too high an exposure factor, described earlier, is thereby eliminated. Under these conditions, there is no longer a maximum or minimum exposure time but only one constant exposure time. The disadvantages of the Schwarzschild effect are also eliminated by this method.

Because the need for long exposure times has been eliminated, all the exposure times can be reduced to the minimum possible, which is very desirable in production.

Run of the mill negatives used in the printing industry generally have a minimum (shadow) density of fairly close to 0.3, so that a present constant exposure effectiveness along any of the curves of FIG. 11 will provide a positive image in which the actual maximum point density of each print is at the level of P. A departure of 0.1 or 0.2 density units from the minimum expected negative density of 0.3 is not frequent and will not make any material difference in the maximum print density.

By selecting a suitable characteristic curve of FIG. 1 for each positive made from the foregoing negatives, the minimum density of each positive can be arranged to fall at the desired density level, preferably 0.3. The selection is readily effected by merely measuring the maximum density of each negative with any densitometer. A very high maximum negative density of 2.5 for example, calls for use of curve 1, a maximum negative density as low as 1.3 for example, calls for use of curve 6, and intermediate maximum negative density values intermediate curves.

It is accordingly a very simple matter to merely measure the maximum density of each negative and then expose it with the appropriate proportion of light colors. Moreover, the thus exposed light-sensitive materials can then be subjected to identical processing treatments so that the developing and all other processing treatments are readily effected with automatic equipment that needs no supervision. Indeed deed the entire copying process including the exposure selection can be made automatic by having a densitometer arranged to automatically scan each negative and generate a voltage signal corresponding to the maximum density of each negative, the voltage signal than automatically selecting the exposure light proportion. A measuring and selecting technique adaptable for such purposes is described in US. Pat. No. 3,531,199.

The two different colors used in the exposure step of the present invention can be taken from any portions of the light spectrum, both visible as well as ultraviolet and infra-red. The visible colors such as red, green and blue or even yellow are preferred in as much as misoperation of the exposure light is then more readily detected. These colors can be generated by separate light sources, or a single light source can be used with an appropriate filter arrangement either fixed in place or shifted in and out of the light path to make the separate colors. Such light sources are also shown in US. Pat. No. 3,531,199. The exposures to the two colors can be made simultaneous or successive, or partially simultaneous and partially simultaneous and partially successive.

FIG. 2 illustrates a special case where characteristic curves for partial exposures do not have exactly the same shadow density as they do for 100 percent exposure with light color L or L but are different by a value indicated by the space between the vertical dashed lines when exposure is carried out with percent L and 40 percent L (curve 3). This difference can be allowed for by a suitable slight shortening or lengthening of the total exposure time when making such partial exposure. If there is, for example, a deviation of about 0.1 log I.t units towards a higher sensitivity (as shown) the proportional exposure times for curve 3 should be shortened to 0.8 times the proportional amounts (log 0.8 0.1).

Since these deviations in the shadow density, which can be easily determined experimentally for a particular copying material, remain within narrow limits and are found in practice not to exceed 0.1 to 0.2 log i.t units, this correction is not difficult. Within such a narrow time interval, the Schwarzschild effect has no effect; if desired, it can be controlled by introducing a constant Schwarzschild exponent.

If the shadow portions of the original negatives which are to be copied show differences in density, these may also be eliminated by a suitable correction to the total exposure.

Thus if a negative has a minimum (shadow) density of 0.6 and the exposure selection was based on an assumed minimum density of 0.3, then it is only necessary to increase the exposure times by a factor of 2.0. This measuring can also be readily made by a densitometer, and the time adjustment made by hand or automatically.

It is, of course, always also possible to bring the different densities of the shadow portions of the negative original (dark portions of the positive) to the same value by interposing or removing a grey filter of suitable density in the path of the light rays of L, and L to level out the density differences in the shadow portion.

However, the two characteristic curves for L l and v L can also'be adjusted during production of the photographic film by suitable spectral sensitization of the two silver halide emulsions so that t is not necessary to use any means for reducing the light, or such use can be limited to a minimum amount of fine adjustment, in contrast to coarse adjustment which is made to the film during production. The copying material can then be out the process according to the invention. Such a material, including its method of production, has been described e.g. in U.S. Pat. No. 2,280,300, British Pat. No.

494,088 or in German Patent Application A 56 772 IX- a/Sflb (published as Offenlegungsschrift 1,597,476). The material according to the British Patent consists, for example, of a mixture of two silver halide emulsions of different gamma which have been produced independently of each other, one of which is asilver chloride emulsion and the othera silver bromide or silver chlorobromide emulsion, the silver chloride emulsion being sensitized to light from the visible spectrum to which the other emulsion is insensitive or less sensitive.

The light-sensitive materials disclosed in the other patent and patent application are of similar composition.

The advantages of the process according to the invention are particularly valuable if an automatic exposure process is used. Since the range of exposuretimes is greatly restricted in the process according to the invention, from 32 to 3.2 according to the figures given below, in other words to one-tenth of the times required in the earlier method of procedure, a more uniform production is possible. The range of exposure times can be kept short in the process according to the invention, and because of such smaller range, the automatic exposure instruments can be simpler in construction, with the result that they are less liable to break down and cheaper to manufacture.

The present invention can also be carried out with a single silver halide emulsion to provide the varying contrast. A copying material having a silver halide emulsion layer with steep gamma-value greater than 4.0 in combination with a colored contact screen provides positive half tone copies whose contrast varies with the color of the copying light in such a manner that a first gamma-value is obtained with a light of color L, and a steeper gamma-value with another light of color L The spectral sensitivity of the said silver halide emulsion layer and/or the relative intensity of the copying lights L, and L used for exposure are adjusted so that for a given exposure time to light of color L or to light of color L and/or partial exposure to L, to L the resulting characteristic curves intersect'at the particular valueto be obtained in the shadow tive copy.

A magenta-colored contact screen is preferred. Phoportions of the positographic materials. with a very steep gamma value are known under the name lithfilm.

The variation of the gamma-value of the half-tone positive is based on the fact that the properties of the colored contact screen depend on the color of light used. Thus the density range which can be covered by the combination of the high contrast emulsion with the colored screen can be adapted to that of the continuous-tone negative original by varying the color of the light source. This is not the case with a normal grey screen.

The density range which a grey contact screen can cover is calculated by subtracting the minimum density between two screen dots from the maximum density of one screen dot. For example the density range a certain type of neutral grey screen is able to reproduce, is from 0.2 to 1.6 or a spread of 1.4. This is the density range which the continuous-tone negative mustpossess to produce a screen positive. with a. minimum dot size of 0 per cent and a maximum dot size of 100 per cent. If

- other minimum and maximum dot sizes are required,

say 5 per cent and 95 per cent respectively, the density range the screenis able to cover will be smaller. Furthermore the calculated density range 1.4 in the example) only applies to an infinite contrast of the high contrast film on which the screen positive is made. Al-

though the contrast of a lithfilm is extremely high (10 to 15 it will certainly not be infinite, so that the actual density range which can be covered by the contact screen will always be greater than the calculated value.

The same rule applied to the calculation of the density range which a colored, e.g., magenta contact screen can cover. However, since the density of a magenta dye depends on the color of the light'with which it is measured, the density range which the magenta screen is able to cover will also be depend on the color of the lightsource. For example one magenta screen when used with a green light shows a density range from 0.4 to 2.1 for a spread of 1.7. The density range which can be covered when using blue light is 0.2 to 1.2, or 1.0..

As explained above it is sometimes desirable to alter the exposure times slightly for the different colors of density value which corresponds to the desired density the emulsion and/or the relative intensity of the two copying lights L, and L may be adjusted, if desired, so that the same exposure time-is used for the curve 1 exposure of FIG. 1 as for the curve 6 exposure in that figure. In those situations where there is no need to make a special correction for mixed exposures as described in connection with FIG. 2, each mixed exposures will then also require the same total exposure time. Such a constant-time exposure is simpler to incorporate into automatic equipment. The resulting characteristic curves of the half-tone image will then intersect at the level of the desired density value D for the shadow portions of the positive copy.

A further description of the present invention and the manner of its use is contained in the book Standardization and Automation with the Gevarex System, published by AgfaGevaert AG, the contents of which are hereby incorporated herein as though fully set forth.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Example 1 An orthochromatic silver chlorobromide gelatin emulsion with a relatively steep gamma-value is applied to one surface of a transparent support of polyethylene terephthalate (thickness 180p). The other side of the support is coated with a non-sensitized, silver iodobromide gelatin emulsion having a relatively flat gamma. A combination of this type is illustrated in FIG. 4 of British Patent No. 494,088.

The adjustment of the material to the conditions of exposure in accordance with the invention is performed as follows: The photographic material described above is exposed to light of color L in a conventional copying apparatus behind a grey wedge through a blue filter which transmits light of a wavelength between 400 and 500 millimicrons, e.g. the blue separation filter B 479 of Agfa-Gevaert AG. Another strip of the material is exposed to light of color L in the same apparatus for the same exposure time through a yellow filter which transmits light of a wavelength down to about 500 millimicrons, e.g. the yellow filter R 519 of Agfa-Gevaert AG. Both strips are developed and processed identically.

Only the characteristic curves of the two copies are measured. These should intersect at the desired density value 1.7 for the density of the shadow portions in the positive copy.

This condition will not generally be met at first. Further adjustment is therefore accomplished as follows:

The copying light for that curve which is too sensitive gives a too high density is combined with a grey filter which has a density value that can be calculated from the characteristic curves by the horizontal distance between the two curves at the density 1.7.

lf repetition of the copying test under the modified conditions shows that the two curves (for L and L now intersect at density value 1.7, the adjustment according to the invention has been achieved and the copying apparatus is ready for use.

The results of tests which illustrate the advantage of the process according to the invention are given in the following Table. The tests were performed with three different negatives which differ in their maximum density and their density range. The properties of the negatives are given in the first two columns of the Table, the minimum and maximum density is given in column 1 and the density range in the second column.

Positive copies of equal density in the light shadow portions and darks were produced from these three negatives by two methods:

According to the procedure in U.S. Pat. No. 3,531,199 characteristic curves which are divergent towards the shadow portions (high density portions) were adjusted to yield the same low highlight density.

Total exposure time in density density minimum maximum range seconds The wide range in exposure timesof 5 to 65.5 seconds (=1 1 3. l) in the prior (the conventional) method of procedure (I) is reduced to the narrow range of between 3.8 seconds and 5.0 seconds (121.3) in the procedure according to the invention (11).

The following are additional example of emulsion combination suitable for use with the present invention.

Example 11 A neutral silver chloride-bromide emulsion prepared by simultaneous addition from separate jets of a silver nitrate solution and a solution of the water-soluble halide mole percent bromide and 15 mole percent chloride containing traces of iodide 0.15 mole percent, average grain size 0.25 micron) into a gelatin solution (emulsion B), was after optimal chemical ripening mixed with a highly sensitive ammoniacal silver bromide-iodide emulsion (emulsion A, having an average grain size 0.8 micron) containing 6.5 mole percent of iodide prepared by a slow addition of ammoniacal silver nitrate in an aqueous solution containing an excess of dissolved halide.

The sensitivity of the emulsion A in the inherent sensitivity region was found to be about 10 times the inherent sensitivity of emulsion B.

The emulsions A and B were mixed in a molar ratio of 2,6621.

The emulsion mixture was spectrally sensitized with 20 mg of the sensitizing dye H C2OOC I (simmer per 0.34 mole of silver halide and was coated at a rate of 0.059 mole of silver halide per square meter after incorporation of the necessary emulsion ingredients such as stabilizing, hardening and wetting agents. Two strips of the light-sensitive material were respectively exposed through the filters U 449 and L 519 the densityversus-wavelength curves of which are given in FIG. 3.

Both strips were developed under the same circumstances and the gradation calculated from the slope of the straight line which was drawn between density 0.3 and density 1.4 of the sensitometric curve.

The following values were obtained: Gamma of 0.62 after exposure through the filter U 449 (exposure in the inherent sensitivity region) Gamma of 1.08 after exposure through the filter L 519 (exposure in the spectral sensitization region).

1 I Exampell Example IV The same emulsion combination and coating conditions were applied as described in Example 11 except that one emulsion portion K was sensitized with 13 mg of the mentioned sensitizing agent and another emulsion portion L having the same silver halide content sensitized with 26 mg of the same sensitizing agent.

After exposure through the indicated filters, the following gamma values were obtained:

Filter U 449 Filter L 519 Emulsion K 0.62 1.15

Emulsion L 0.63 1.15

Example V A highly sensitive silver bromideiodide emulsion containing 6 mole percent of iodide prepared by a separate addition of a silver nitrate solution aand potassium iodide in an excess of bromide was mixed in a molar ratio of 3 to 1 with a silver chloride bromide emulsion of the acid type containing 70 mole percent of bromide and 30 mole percent of chloride.

The emulsion mixture was spectrally sensitized with 12 mg of the sensitizing dye Example VI A bromide-iodide emulsion prepared as described in Example V was mixed in a ratio of 3 to 1 with a silver chloride bromide emulsion prepared by double jet precipitation containing mole percent of chloride and 40 mole percent of bromide.

The emulsion mixture was spectrally sensitized with 12 mg ot the sensitizing dye of Example V per 0.24 mole of silver halide and coated at a rate of 0.047 mole of silver halide per square meter.

Upon exposure through filter U 449 and L 519 gammavalues of 0.84 and 1.78 were obtained, respectively.

What is claimed is:

1. In the preparation of positive photographic continuous tone images having substantially equal low density in the highlights and substantially equal high density in the shadow portions from a plurality of black and white negative continuous tone originals of different density range but density of the shadow portions within a minimum deviation range in which a light-sensitive silver halide emulsion, which is spectrally sensitized to yield a first flat gamma when exposed to a first light of wavelengths in a given spectral range and a second steep gamma when exposed to a second light of wavelengths of a different given spectral range and to yield intermediate gamma when exposed to proportions of said first and second light wavelengths between said first and second wavelengths, is prepared, the emulsion is applied to a stable support, exposing the negative originals to the emulsion in light composed of proportions of said first and said second light wavelengths in the range of from between said first and said second wavelengths and subjecting the exposed emulsion to photographic processing including development and fixing in suitable baths, the improvement according to which the maximum density of each copied negative original is measured prior to exposure, adjusting the relative portions of the wavelengths of the light for the exposure of each negative original to obtain characteristic curves of the developed emulsion said characteristic curves each having the same high density value, said common point of the light to provide a steep gamma value within the per 0.24 mole of silver halide and coated at a rate of 0.047 mole of silver halide per sq. m.

Upon exposure of such emulsion through filter U 449 and L 519 gamma values of 0.84 and 1.90 were obtained. respectively.

range of 1.3 and 1.8 in the developed emulsion and developing and fixing the thus-exposed emulsion for each of the negative originals.

2. Process of claim 1 wherein one silver halide emulsion is an orthochromatically sensitizing silver halide gelatin emulsion and the second is a blue sensitive silver halide emulsion and wherein the light comprises light from the green and blue range of the visible spectrum.

3. The process of claim 1 in which the negative originals have densities in the shadow positions of approximating 0.3.

4. In the preparation of positive photographic continuous tone images having substantially equal low density in the highlights and substantially equal high density in the shadow portions from a plurality of black and white continuous tone originals of different density range but density of the shadow portions within a minimum deviation range in which a silver halide emulsion layer which is spectrally sensitized to yield a gamma greater than 4.0 is prepared with a magenta contact screen, and the emulsion is applied to a stable support, exposing the emulsion to the negative originals in copying lights composed of proportions of a first and a second light wavelengths in a given spectral range to which the emulsion is sensitive and subjecting the exposed emulsion to photographic processing including development and fixing in suitable baths, wherein the improvement comprises the maximum density of each copied negative original is measured prior to exposure, adjusting the relative portions of the wavelengths of light for the exposure of each of the negative originals to obtain characteristic curves of the developed emulsion, said characteristic curves each having the same high density value, said common point high density value being within the range of 1.5 to 2.0 under said common exposure time, which value is within the range of from 1.5 to 2.0 when using substantially the same total exposure time for each negative, exposing each of the negative originals to the lightsensitive emulsion to the proportioned light for said common exposure time so as to provide a contrast range of the positive copy that brings the highlight densities to substantially the same low level. 

1. IN THE PREPARATION OF POSITIVE PHOTOGRPAHIC CONTINUOUS TONE IMAGES HAVING SUBSTANTIALLY EQUAL LOW DENSITY IN THE HIGHLIGHTS AND SUBSTANTIALLY EQUAL HIGH DENSITY IN THE SHADOW PORTIONS FROM A PLURALITY OF BLACK AND WHITE NEGATIVE CONTINUOUS TONE ORIGNALS OF DIFFERENT DENSITY RANGE BUT DENSITY OF THE SHADOW PORTIONS WITHIN A MINIMUM DEVIATION RANGE IN WHICH A LIGHT-SENSTIVE SILVER HALIDE EMULSION, WHICH IS SPECTRALLY SENSITIZED TO YIELD A FIRST FLAT GAMMA WHEN EXPOSED TO A FIRST LIGHT OF WAVELENGTHS IN A GIVEN SPECTRAL RANGE AND A SECOND STEEP GAMMA WHEN EXPOSED TO PROPORTIONS OF SAID FIRST AND SECOND OF A DIFFERENT GIVEN SPECTRAL RANGE AND TO YIELD INTERMEDIATE GAMMA WHEN EXPOSED TO PROPORTIONS OF SAID FIRST AND SECOND LIGHT WAVELENGTHS BETWEEN SAID FIRST AND SECOND WAVELENGTHS, IS PREPARED, THE EMULSION IS APPLIED TO A STABLE SUPPORT, EXPOSING THENEGATIVE ORIGINALS TO THE EMULSION IN LIGHT COMPOSED OF PROPORTIONS OF SAID FIRST AND SAID SECOND LIGHT WAVELENGHTS IN THE RANGE OF FROM BETWEEN SAID FIRST AND SAID SECOND WAVELENGTHS AND SUBJECTING THE EXPOSED EMULSION TO PHOTOGRAHIC PROCESSING INLCUDING DEVELOPMENT AND FIXINNG IN SUITABLE BATHS, THE IMPROVEMENT ACCORDING TO WHICH THE MAXIMUM DENSITY OF EACH COPIED NEGATIVE ORIGINAL IS MEAURED PRIOR TO EXPOSURE, ADJUSTING THE RELATIVE PORTIONS OF THE WAVELENGTHS OF THE LIGHT FOR THE EXPOSURE OF EACH NEGATIVE ORIGINAL TO OBTAIN CHARACTER ISTIC CURVES OF THE DEVELOPED EMULSION SAID CHARACTERISTIC CURVES EACH HAVING THE SAME HIGH DENSITY VALUE, SAID COMMON POINT HIGH DENSITY VALUE BEING WITHIN THE RANGE OF 1.5 TO 2.0 UNDER SAID COMMON EXPOSURE TIME USING WITH EACH XPOSURE AN EXPOSURE TIME WITHIN A MINIMUM DEVIATION, EXPOSING EACH OF THE NEGATIVE ORIGINALS TO THE LIGHT-SENSITIVE EMULSION TO THE PROPORTIONED LIGHT FOR SAID COMMON EXPOSURE TIME TO PROVIDE A FLAT GAMMA VALUE WITHIN THE RANGE OF 0.5 TO 0.9 IN THE DEVELOPED EMULSION EXPOSING THE LIGHT-SENSITIVE EMULSION TO A PORTION OF THE LIGHT TO PROVIDE A STEEP GAMMA VALUE WITHIN THE RANGE OF 1.3 AND 1.8 IN THE DEVELOPED EMULSION AND DEVELOPING AND FIXING THE THUS-EXPOSE EMULSION FOR EACH O THE NEGATIVE ORIGINALS.
 2. Process of claim 1 wherein one silver halide emulsion is an orthochromatically sensitizing silver halide gelatin emulsion and the second is a blue sensitive silver halide emulsion and wherein the light comprises light from the green and blue range of the visible spectrum.
 3. The process of claim 1 in which the negative originals have densities in the shadow positions of approximating 0.3.
 4. In the preparation of positive photographic continuous tone images having substantially equal low density in the highlights and substantially equal high density in the shadow portions from a plurality of black and white continuous tone originals of different density range but density of the shadow portions within a minimum deviation range in which a silver halide emulsion layer which is spectrally sensitized to yield a gamma greater than 4.0 is prepared with a magenta contact screen, and the emulsion is applied to a stable support, exposing the emulsion to the negative originals in copying lights composed of proportions of a first and a second light wavelengths in a given spectral range to which the emulsion is sensitive and subjecting the exposed emulsion to photographic processing including development and fixing in suitable baths, wherein the improvement comprises the maximum density of each copied negative original is measured prior to exposure, adjusting the relative portions of the wavelengths of light for the exposure of each of the negative originals to obtain characteristic curves of the developed emulsion, said characteristic curves each having the same high density value, said common point high density value being within the range of 1.5 to 2.0 under said common exposure time, which value is within the range of from 1.5 to 2.0 when using substantially the same total exposure time for each negative, exposing each of the negative originals to the lightsensitive emulsion to the proportioned light for said common exposure time so as to provide a contrast range of the positive copy that brings the highlight densities to substantially the same low level. 